Abstract: Microscale model test technology has the advantages of small scale, short test cycle and good economical efficiency. It can be used to study the river-lake relationships of large-scale and complex systems. However, there are few domestic application examples. The key technical issues associated with similarity theory and microscale model design need to be further studied. Based on the need of studying the law of backflow from the Yangtze River into Poyang Lake, in this paper, we discuss the similarity laws and the design method of the microscale model which should be followed in the microscale mode for backflow from the Yangtze River into Poyang Lake, put forward the solution of the resistance similarity of the microscale model and the measurement and control of the physical quantities of the model, and establish a microscale model for the Yangtze River-Poyang Lake-tail channels of "five Rivers" in Jiangxi with the horizontal scale of 1:6 500 and the vertical scale of 1:150. Through the verification of the measured hydrological data, the microscale model shows a good similarity with the prototype in terms of water level, flow velocity and duration and flow rate of water from the Yangtze River flowing backward into Poyang Lake. The model design and simulation method proposed in this paper provide a theoretical basis for further promotion of the microscale model test technology and provide reference for the study of the large-scale and complex water-sediment movement problems of rivers, lakes, estuaries and coasts.